gnu: Add libxml++-3.

* gnu/packages/gnome.scm (libxml++-3): New variable.

Change-Id: I2250766126f433b3f5dcc50cd7eaadec3acadad3

gnu/packages/gnome.scm

@@ -8768,8 +8768,25 @@ the available networks and allows users to easily switch between them.")
 library.")
     (license license:lgpl2.1+)))
 
-;; This is the last release providing the 2.6 API, hence the name.
 ;; This is needed by tascam-gtk
+(define-public libxml++-3
+  (package
+    (inherit libxml++)
+    (name "libxml++")
+    (version "3.2.4")
+    (source
+     (origin
+       (method git-fetch)
+       (uri (git-reference
+             (url "https://github.com/libxmlplusplus/libxmlplusplus")
+             (commit version)))
+       (file-name (git-file-name name version))
+       (sha256
+        (base32 "07f6l9ka63dnc85npxq5g7bn1ja7lad0w2wixqdlyabdvc4l2hp5"))))
+    (propagated-inputs (modify-inputs (package-propagated-inputs libxml++)
+                         (append glibmm-2.64)))))
+
+;; This is the last release providing the 2.6 API, hence the name.
 (define-public libxml++-2
   (package
     (inherit libxml++)